[newlib-cygwin] Cygwin: pty: Use redraw screen instead of clear screen.

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=7ef4290a98edca60cfbab44327384f8ad6b471da

commit 7ef4290a98edca60cfbab44327384f8ad6b471da
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Tue Nov 12 22:00:23 2019 +0900

    Cygwin: pty: Use redraw screen instead of clear screen.
    
    - Previously, pty cleared screen at startup for synchronization
      between the real screen and console screen buffer for pseudo
      console. With this patch, instead of clearing screen, the screen
      is redrawn when the first native program is executed after pty
      is created. In other words, synchronization is deferred until
      the native app is executed. Moreover, this realizes excluding
      $TERM dependent code.

Diff:
---
 winsup/cygwin/fhandler_tty.cc | 30 ++++++++++++++++--------------
 winsup/cygwin/tty.cc          |  2 +-
 winsup/cygwin/tty.h           |  2 +-
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc
index c716030..e02a8f4 100644
--- a/winsup/cygwin/fhandler_tty.cc
+++ b/winsup/cygwin/fhandler_tty.cc
@@ -2669,7 +2669,7 @@ fhandler_pty_slave::fixup_after_attach (bool native_maybe, int fd_set)
 	  if (get_ttyp ()->num_pcon_attached_slaves == 0
 	      && !ALWAYS_USE_PCON)
 	    /* Assume this is the first process using this pty slave. */
-	    get_ttyp ()->need_clear_screen = true;
+	    get_ttyp ()->need_redraw_screen = true;
 
 	  get_ttyp ()->num_pcon_attached_slaves ++;
 	}
@@ -2700,6 +2700,21 @@ fhandler_pty_slave::fixup_after_attach (bool native_maybe, int fd_set)
 		  kill (get_ttyp ()->pcon_pid, 0) != 0)
 		get_ttyp ()->pcon_pid = myself->pid;
 	      get_ttyp ()->switch_to_pcon_out = true;
+
+	      if (get_ttyp ()->need_redraw_screen)
+		{
+		  /* Forcibly redraw screen based on console screen buffer. */
+		  /* The following code triggers redrawing the screen. */
+		  CONSOLE_SCREEN_BUFFER_INFO sbi;
+		  GetConsoleScreenBufferInfo (get_output_handle (), &sbi);
+		  SMALL_RECT rect = {0, 0,
+		    (SHORT) (sbi.dwSize.X -1), (SHORT) (sbi.dwSize.Y - 1)};
+		  COORD dest = {0, 0};
+		  CHAR_INFO fill = {' ', 0};
+		  ScrollConsoleScreenBuffer (get_output_handle (),
+					     &rect, NULL, dest, &fill);
+		  get_ttyp ()->need_redraw_screen = false;
+		}
 	    }
 	  init_console_handler (false);
 	}
@@ -2717,19 +2732,6 @@ fhandler_pty_slave::fixup_after_fork (HANDLE parent)
   // fork_fixup (parent, inuse, "inuse");
   // fhandler_pty_common::fixup_after_fork (parent);
   report_tty_counts (this, "inherited", "");
-
-  if (get_ttyp ()->need_clear_screen)
-    {
-      const char *term = getenv ("TERM");
-      if (term && strcmp (term, "dumb") && !strstr (term, "emacs"))
-	{
-	  /* FIXME: Clearing sequence may not be "^[[H^[[J"
-	     depending on the terminal type. */
-	  DWORD n;
-	  WriteFile (get_output_handle_cyg (), "\033[H\033[J", 6, &n, NULL);
-	}
-      get_ttyp ()->need_clear_screen = false;
-    }
 }
 
 void
diff --git a/winsup/cygwin/tty.cc b/winsup/cygwin/tty.cc
index 460153c..9c66b89 100644
--- a/winsup/cygwin/tty.cc
+++ b/winsup/cygwin/tty.cc
@@ -244,7 +244,7 @@ tty::init ()
   pcon_pid = 0;
   num_pcon_attached_slaves = 0;
   term_code_page = 0;
-  need_clear_screen = false;
+  need_redraw_screen = false;
 }
 
 HANDLE
diff --git a/winsup/cygwin/tty.h b/winsup/cygwin/tty.h
index 927d7af..a6732ae 100644
--- a/winsup/cygwin/tty.h
+++ b/winsup/cygwin/tty.h
@@ -105,7 +105,7 @@ private:
   pid_t pcon_pid;
   int num_pcon_attached_slaves;
   UINT term_code_page;
-  bool need_clear_screen;
+  bool need_redraw_screen;
 
 public:
   HANDLE from_master () const { return _from_master; }